The mechanisms of α-H and proton transfers of glycine induced by Mg2+

2015 ◽  
Vol 14 (02) ◽  
pp. 1550008
Author(s):  
Qing Zhang ◽  
Xiang-Jun Meng
Keyword(s):  
Energy Barrier ◽  
Inductive Effect ◽  
Covalent Bond ◽  
Electron Cloud ◽  
Chemical Activity ◽  
The Other ◽  
Single Bond ◽  
Substitution Reactions ◽  
Neutral Complex ◽  
Proton Transfers

A MP2/6-31++G(d,p)//B3LYP/6-31++G(d,p) method was used to investigate the mechanisms of α- H and proton transfers of glycine induced by Mg 2+. Eight complexes were obtained, six of which were neutral and the other two were zwitterionic. Among them, the zwitterion with a binding energy of 159.4 kcal/mol was the most stable structure. Conformation transformations of the complexes caused by the rotation of single bond and the transfers of α- H and proton were completed via seven transition states. The inductive effect of Mg 2+ made the electron cloud of glycine deviate to Mg 2+, which activated the covalent bond involving the transferred proton. The neutral complex can be turned into the zwitterionic one by the transfers of both carboxyl hydrogen and α- H , and the energy barrier of each reaction was less than 9.2 kcal/mol. After the transfer of α- H , a delocalized π bond was formed in glycine skeleton and the α- C atom took 0.19 positive charges. So the chemical activity of the glycine enhanced, and glycine was readily available for addition and nucleophilic substitution reactions. The path from the most stable glycine conformer G1 to the zwitterionic conformation I is G1 → G1–G3 → G3 → G3–G4 → G4 → G2–G4 → G2 → VI → I–VI → I, and the highest energy barrier of this path is 9.2 kcal/mol.

Reactions of macroions with ester and carboxylic groups of polymers

1987 ◽  
Vol 52 (9) ◽  
pp. 2194-2203
Author(s):  
Miloslav Kučera ◽  
Dušan Kimmer ◽  
Karla Majerová ◽  
Josef Majer
Keyword(s):  
Maleic Anhydride ◽  
Acrylic Acid ◽  
Methyl Methacrylate ◽  
Bond Formation ◽  
Covalent Bond ◽  
The Other ◽  
Poly Methyl Methacrylate ◽  
Other Hand ◽  
Carboxylic Groups ◽  
Poly Acrylic Acid

In the reaction of dianions with poly(methyl methacrylate), only an insignificant amount of insoluble crosslinked product is obtained. If, however, the concentration of grafting dianions approaches that of ester groups, the amount of poly(methyl methacrylate) which may thus be crosslinked becomes quite significant. Dications, too, can bring about crosslinking of only an insignificant number of poly(methyl methacrylate) chains. Carboxylic groups in poly(acrylic acid) react with dianions and dications in an anhydrous medium similarly to ester groups. On the other hand, in the presence of a cocatalytic amount of water dications are more readily bound to carboxylic groups, forming a covalent bond. The relatively highest efficiency was observed in the bond formation between dication and the poly[styrene-alt-(maleic anhydride)], both in an anhydrous medium and in the presence of H2O.

Buckling Design of Axially Compressed Cylindrical Shells Based on Energy Barrier Approach

2021 ◽  
pp. 2150165
Author(s):  
Haigui Fan ◽  
Wenguang Gu ◽  
Longhua Li ◽  
Peiqi Liu ◽  
Dapeng Hu
Keyword(s):  
Experimental Data ◽  
Energy Barrier ◽  
Thin Shell ◽  
Design Method ◽  
Lightweight Design ◽  
Cylindrical Shells ◽  
Design Criterion ◽  
The Other ◽  
Shell Structures ◽  
Buckling Loads

Buckling design of axially compressed cylindrical shells is still a challenging subject considering the high imperfection-sensitive characteristic in this kind of structure. With the development of various design methods, the energy barrier concept dealing with buckling of imperfection-sensitive cylindrical shells exhibits a promising prospect in recent years. In this study, buckling design of imperfection-sensitive cylindrical shells under axial compression based on the energy barrier approach is systematically investigated. The methodology about buckling design based on the energy barrier approach is described in detail first taking advantage of the cylindrical shells whose buckling loads have been extensively tested. Then, validation and discussion about this buckling design method have been carried out by the numerical and experimental analyses on the cylindrical shells with different geometrical and boundary imperfections. Results in this study together with the available experimental data have verified the reliability and advantage of the buckling design method based on energy barrier approach. A design criterion based on the energy barrier approach is therefore established and compared with the other criteria. Results indicate that buckling design based on energy barrier approach can be used as an efficient way in the lightweight design of thin-shell structures.

Mesitylene Osmium(II) Complexes Containing the Functional Phosphane tBuP(CH2CO2Me)2 and Anionic Species Derived Thereof as Bi- and Tridentate Ligands

1998 ◽  
Vol 53 (5-6) ◽  
pp. 540-544 ◽  
Author(s):  
Gerhard Henig ◽  
Helmut Werner
Keyword(s):  
Membered Ring ◽  
Chelate Complex ◽  
The Other ◽  
Quantitative Yield ◽  
Partial Hydrolysis ◽  
Neutral Complex ◽  
Ligand Complex ◽  
Tridentate Ligands ◽  
Tripodal Ligand ◽  
Anionic Species

Abstract The dichloroosmium(II) compound [(mes)OsCl2(L)] (2) with L = tBuP(CH2CO2Me)2 reacts with one or two equivalents of AgPF6 to give the mono- or dicationic complexes 3 and 4 containing the phosphanediyldiester as a bi- or tridentate chelating ligand. Complex 4 undergoes, in the presence of water, partial hydrolysis to give the difluorophosphatoosmium(II) derivative 5 in quantitative yield. Treatment of 4 with two equivalents of KOtBu affords by deprotonation at both CH2 groups of L the neutral complex 6, in which one PCHCO2Me unit of the dianionic ligand |tBuP(CHCO2Me)2]2- forms a five-membered and the other PCHCO2Me unit a three-membered ring with the metal. The reaction of 6 with water leads selectively to the formation of the chelate complex 7 containing the phosphanediylbis(carboxylate) [tBuP(CH2CO2)2]2- as a tripodal ligand.

scholarly journals How Far Can One Push the Noble Gases Towards Bonding?: A Personal Account

Molecules ◽  
2019 ◽  
Vol 24 (16) ◽  
pp. 2933 ◽  
Author(s):  
Ranajit Saha ◽  
Gourhari Jana ◽  
Sudip Pan ◽  
Gabriel Merino ◽  
Pratim Kumar Chattaraj
Keyword(s):  
Electron Density ◽  
High Pressures ◽  
Noble Gases ◽  
Activation Barrier ◽  
Covalent Bond ◽  
The Other ◽  
Personal Account ◽  
Covalent Bonds ◽  
Other Hand ◽  
Different Types

Noble gases (Ngs) are the least reactive elements in the periodic table towards chemical bond formation when compared with other elements because of their completely filled valence electronic configuration. Very often, extreme conditions like low temperatures, high pressures and very reactive reagents are required for them to form meaningful chemical bonds with other elements. In this personal account, we summarize our works to date on Ng complexes where we attempted to theoretically predict viable Ng complexes having strong bonding to synthesize them under close to ambient conditions. Our works cover three different types of Ng complexes, viz., non-insertion of NgXY type, insertion of XNgY type and Ng encapsulated cage complexes where X and Y can represent any atom or group of atoms. While the first category of Ng complexes can be thermochemically stable at a certain temperature depending on the strength of the Ng-X bond, the latter two categories are kinetically stable, and therefore, their viability and the corresponding conditions depend on the size of the activation barrier associated with the release of Ng atom(s). Our major focus was devoted to understand the bonding situation in these complexes by employing the available state-of-the-art theoretic tools like natural bond orbital, electron density, and energy decomposition analyses in combination with the natural orbital for chemical valence theory. Intriguingly, these three types of complexes represent three different types of bonding scenarios. In NgXY, the strength of the donor-acceptor Ng→XY interaction depends on the polarizing power of binding the X center to draw the rather rigid electron density of Ng towards itself, and sometimes involvement of such orbitals becomes large enough, particularly for heavier Ng elements, to consider them as covalent bonds. On the other hand, in most of the XNgY cases, Ng forms an electron-shared covalent bond with X while interacting electrostatically with Y representing itself as [XNg]+Y−. Nevertheless, in some of the rare cases like NCNgNSi, both the C-Ng and Ng-N bonds can be represented as electron-shared covalent bonds. On the other hand, a cage host is an excellent moiety to examine the limits that can be pushed to attain bonding between two Ng atoms (even for He) at high pressure. The confinement effect by a small cage-like B12N12 can even induce some covalent interaction within two He atoms in the He2@B12N12 complex.

The Mass Spectrometry of the Pyrolysis Products of Some Tetraalkylammonium and Bistetraalkylammonium Bromides

1974 ◽  
Vol 52 (19) ◽  
pp. 3438-3443 ◽  
Author(s):  
Ronald E. Verrall ◽  
John A. Burns
Keyword(s):  
Mass Spectra ◽  
Inductive Effect ◽  
Alkyl Halide ◽  
Substitution Reactions ◽  
Pyrolysis Products ◽  
Quaternary Nitrogen ◽  
Tetraalkylammonium Bromide ◽  
Pyrolytic Decomposition ◽  
Major Process ◽  
Positively Charged

The mass spectra of three tetraalkylammonium bromide salts and two series of bistetraalkylammonium bromide salts, one saturated and the other unsaturated, have been studied. Substitution is the major process which occurs in the pyrolytic decomposition of these quaternary ammonium bromides when placed in the probe of the mass spectrometer. This leads to the production of a tertiary amine and an alkyl halide. The substitution reactions which occur are influenced by the proximity of the bromide anion(s) to the positively charged quaternary nitrogen centers in the crystal lattice. As well, a shorter distance between the positive nitrogen centers favors substitution reaction by means of an electron inductive effect.

scholarly journals Caryolene-forming carbocation rearrangements

2013 ◽  
Vol 9 ◽  
pp. 323-331 ◽  
Author(s):  
Quynh Nhu N Nguyen ◽  
Dean J Tantillo
Keyword(s):  
Density Functional Theory ◽  
Proton Transfer ◽  
Energy Barrier ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Intramolecular Proton Transfer ◽  
The Other ◽  
Orbital Symmetry ◽  
Functional Theory ◽  
Biosynthetic Precursor

Density functional theory calculations on mechanisms of the formation of caryolene, a putative biosynthetic precursor to caryol-1(11)-en-10-ol, reveal two mechanisms for caryolene formation: one involves a base-catalyzed deprotonation/reprotonation sequence and tertiary carbocation minimum, whereas the other (with a higher energy barrier) involves intramolecular proton transfer and the generation of a secondary carbocation minimum and a hydrogen-bridged minimum. Both mechanisms are predicted to involve concerted suprafacial/suprafacial [2 + 2] cycloadditions, whose asynchronicity allows them to avoid the constraints of orbital symmetry.

scholarly journals The Effect of Molybdenum on Precipitation Behaviour in Austenitic Strip-Cast Steels Containing Niobium

2020 ◽  
Author(s):  
Lu Jiang ◽  
Ross Marceau ◽  
Thomas Dorin ◽  
Huaying Yin ◽  
Xinjun Sun ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Transmission Electron Microscopy ◽  
Energy Barrier ◽  
The Other ◽  
Transmission Electron ◽  
Cast Steels ◽  
Precipitation Behaviour ◽  
Strip Cast ◽  
Electron Energy Loss

Two low-C steels microalloyed with Nb were fabricated by simulated strip casting, one with Mo and the other without Mo. Both alloys were coiled at 900 °C to investigate the effect of Mo on the precipitation behaviour in austenite in low-C strip-cast Nb steels. The mechanical properties results show that during the coiling at 900 °C the hardness of both alloys increases and reaches a peak after 3000 s and then decreased after 10,000 s. Additionally, the hardness of the Mo-containing alloy is higher than that of the Mo-free alloy in all coiling conditions. Thermo-Calc predictions suggest that MC-type carbides exist in equilibrium at 900 °C, which are confirmed by transmission electron microscopy (TEM). TEM examination shows that precipitates are formed after 1000 s of coiling in both alloys and the size of the particles is refined by the addition of Mo. Energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) reveal that the carbides are enriched in Nb and N. The presence of Mo is also observed in the particles in the Nb-Mo steel during coiling. The concentration of Mo in the precipitates decreases with increasing particle size and coiling time. The precipitates in the Nb-Mo steel provide significant strengthening increments of up to 140 MPa, much higher than that in the Nb steel, ~ 96 MPa. A thermodynamic rationale is given, which explains that the enrichment of Mo in the precipitates reduces the interfacial energy between precipitates and matrix. This is likely to lower the energy barrier for their nucleation and also reduce the coarsening rate, thus leading to finer precipitates during coiling at 900 °C.

scholarly journals Relevance of single cell and single molecule studies at different biological and physical length scales

2017 ◽  
Author(s):  
Wenfa Ng
Keyword(s):  
Quantum Mechanics ◽  
Single Cell ◽  
Single Molecule ◽  
Active Site ◽  
Covalent Bond ◽  
The Other ◽  
Quantum Mechanical ◽  
Microfluidic Channels ◽  
Other Hand ◽  
Single Molecule Studies

Scale transcends multiple levels of biological and physical organization, and is the critical factor that determines success of any scientific investigation. Specifically, the scale at which a question is posed plays a crucial role in influencing the type of experiments and apparatuses needed. Single cell and single molecule experiments came to the fore of experiment science due to its capability at addressing a fundamental problem in biology and physical science: does the same behavior in cells and molecules transcend different length and population scales? Thus far, single cell experiments could be achieved with trapping of single cell using optical tweezer traps and microfluidic channels. The same, however, is not true for single molecule studies, which remains in the realm of theoretical and simulation studies. Specifically, single molecule experiment remains at the hundreds to thousands of molecules level, where possible skew in the population of molecules sampled could provide a false depiction of molecular reality of a larger population. But, what do scientists learn from single cell and single molecule studies? Is it the uncovering of mysteries of the probabilistic behavior at the single entity level, guided by perhaps quantum mechanics? The answer is no for single cell studies, given that cellular decision making require the input of tens to hundreds of molecular sensors and effectors within a cell. Hence, single cell behavior is not random, but directed at a nutrient or concentration gradient or signaling source. On the other hand, enzymatic catalysis of a single molecule substrate with the active site involves a quantum mechanical crosstalk. Thus, reaction between the substrate molecule and the active site proceeds if suitable energy levels (i.e., quantum mechanical states) are found for both parties. Given that distribution of quantum mechanical states is probabilistic, stochasticity rules single molecule interaction such as a covalent bond formation reaction between reactant A and B. Thus, single cell and single molecule studies do hold relevance in biological and physical sciences research if the correct experiment tool is used for a pertinent question at an appropriate length and population scale. For example, while tremendous amount of basic understanding could be derived from single cell experiments, single cell perspective is not relevant to questions examining the interactions between two large subpopulations of cells. Single molecule experiments, on the other hand, remains in the theoretical and simulation realm for highlighting the effect of quantum mechanics in guiding the behavior of molecules at the nanoscale.

scholarly journals Interrelated Mechanism by Which the Methide Quinone Celastrol, Obtained from the Roots of Tripterygium wilfordii, Inhibits Main Protease 3CLpro of COVID-19 and Acts as Superoxide Radical Scavenger

2020 ◽  
Vol 21 (23) ◽  
pp. 9266
Author(s):  
Francesco Caruso ◽  
Manrose Singh ◽  
Stuart Belli ◽  
Molly Berinato ◽  
Miriam Rossi
Keyword(s):  
Density Functional ◽  
Superoxide Radical ◽  
Covalent Bond ◽  
Radical Scavenger ◽  
X Ray Diffraction ◽  
Dft Methods ◽  
Functional Theory ◽  
Redox Biology ◽  
Proton Transfers ◽  
Main Protease

We describe the potential anti coronavirus disease 2019 (COVID-19) action of the methide quinone inhibitor, celastrol. The related methide quinone dexamethasone is, so far, among COVID-19 medications perhaps the most effective drug for patients with severe symptoms. We observe a parallel redox biology behavior between the antioxidant action of celastrol when scavenging the superoxide radical, and the adduct formation of celastrol with the main COVID-19 protease. The related molecular mechanism is envisioned using molecular mechanics and dynamics calculations. It proposes a covalent bond between the S(Cys145) amino acid thiolate and the celastrol A ring, assisted by proton transfers by His164 and His41 amino acids, and a π interaction from Met49 to the celastrol B ring. Specifically, celastrol possesses two moieties that are able to independently scavenge the superoxide radical: the carboxylic framework located at ring E, and the methide-quinone ring A. The latter captures the superoxide electron, releasing molecular oxygen, and is the feature of interest that correlates with the mechanism of COVID-19 inhibition. This unusual scavenging of the superoxide radical is described using density functional theory (DFT) methods, and is supported experimentally by cyclic voltammetry and X-ray diffraction.

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